The present invention relates in general to active vibration control systems such as active noise cancellers and, more specifically, to monitoring the operating status of a machine for which undesired vibrations are being cancelled by an active control system.
Active vibration control (also called active noise control) is a technique wherein undesired noise or other vibrations in an area are reduced or eliminated by adding equal and opposite vibrations (counter-vibrations) into the same area. Thus, a pickup sensor converts the undesired vibrations into electrical signals which are applied to a digital computer for calculating the necessary counter-vibrations which will cancel the undesired vibrations. A signal representing the counter-vibrations is coupled to an actuator which applies vibrations to the area where cancellation is to occur. In the case of audible noise, the vibrations to be cancelled are vibrations in air which are sensed by a microphone and are cancelled by inverse noise created by a speaker.
Active vibration control can potentially be used to reduce or eliminate undesirable vibrations (either sound travelling in air or vibrations transmitted mechanically through solid structures) in a wide variety of applications. In the automotive field, such applications include engine exhaust noise, engine mounts, body mounts, vehicle suspension, interior noise, and others.
In many instances where an active vibration control system is employed, the undesired vibrations are created by a machine (i.e., a device having relatively moving parts creating the vibrations while doing work), such as an internal combustion engine, a fan, a pneumatic pump or other device. These machines are often complicated systems themselves, and in many cases it is desirable to monitor and automatically diagnose the operating status of the machine. For example, internal combustion engines in today's automobiles are very complicated machines employing monitoring of complex emission systems and various performance parameters. Certain fault conditions, such as cylinder misfires, must be diagnosed during engine operation to protect emissions systems components, such as a catalytic converter. Thus, co-pending application Ser. No. 07/892,883, now U.S. Pat. No. 5,193,513 misfire detection system using an exhaust pressure transducer and a pattern classifier such as a neural network to perform engine diagnosis.
Both active vibration cancellation systems and machine diagnostic systems can be relatively expensive since they often require specialized hardware and significant computing power.